The present invention generally relates to a cyber-physical method, apparatus, and system for converting kinetic energy from a fluid flow. More particularly, the present invention provides a system for interacting with or manipulating a fluid flow to attain one or more optimization objectives.
Marine and hydrokinetic tidal energy, or kinetic energy of flowing water, has great potential, especially in the United States. Generally, hydrokinetic energy in the United States is largely located near densely populated areas, and as a result, has yet to be significantly harnessed.
Unlike other renewable energy sources like wind and solar, the availability of hydro-kinetic energy is highly predictable and not associated with harmful emissions. The density of hydrokinetic energy in regions of reasonably fast flows is high, and unlike wind energy, the turbulent flow fluctuations are expected to be low so dynamic loading and material fatigue is less of a concern for hydrokinetic power.
Many of the currently available technologies for hydrokinetic energy conversion are statically optimized for a fixed set of operating conditions and are unable to adapt to ever changing environments and circumstances. The vast majority of the currently available technologies employ a rotating turbine for energy capture from the flow. These systems are static and have a single design criteria, to maximize power conversion at the design flow speeds. Since each site for tidal hydro-kinetic power conversion is unique, and the conditions at that site vary over tidal, lunar, an solar cycles, turbines designed for one location cannot be installed in another without expensive redesign or reconfiguration.
Referring to FIG. 1, for example, an installed turbine is shown. The turbines all borrow technology from their close cousins, wind turbines and this technology is relatively mature. Most aero- and hydro-dynamic technologies that exist today (aircraft wings and blades, propellers, turbines, sails) are designed to operate under steady or quasi-steady conditions, and extreme care is taken to mitigate any unsteadiness in their operation.
In such tidal turbines, the flow of oncoming water deflects the turbine blades and because the blades are pivoted at the center of the turbine, causes them to rotate. Fundamental fluid dynamics imposes a bound of about 59%, called the Betz limit, on the highest efficiency with which such turbines can extract the energy of the impinging flow. Current turbines perform with an efficiency close to the Betz limit only when the flow speed is close to a designed speed due to their fixed blade design. Shrouded turbines can improve upon this limit, but at significant structural (and financial) cost.
However, engineering efficiency for fixed flow conditions is not a suitable metric for determining economic feasibility. There are several drawbacks to fixed design tidal turbines. Firstly, they need to be designed and optimized for site-specific target conditions. Such an optimization not only means that a careful, time-consuming and expensive site survey needs to be carried out to identify potential site. A design that is easily adaptable and does not need hardware tuning is economically desirable because then economy of scale can be used for reducing installation costs.
Referring to FIG. 2, the second and largely unforeseen reason for the unattractiveness of fixed design turbines is that desired characteristics of the turbines may change in the future, not only due to environmental changes but also due to large scale deployment of tidal power farms themselves. Turbines extract energy by modifying the flow, thus it is expected that as tidal turbine farms grow, the local flow around each turbine may be completely different. A single turbine designed for the undisturbed site may become completely unsuitable as more turbines are installed and the local flow environment changes. A turbine design that can adapt to its neighboring turbines and can adjust its operating behavior as the farm grows would provide substantial economic advantages. Also, the diameter of a rotary turbine is limited by the depth of water at the site, which is very low at tidal energy hotspots. Moreover, the rotary turbines interfere with each other if they are close to each other, and that means a lot of flow kinetic energy is lost from between the turbines.
Conservation of marine ecology provides yet another concern for rotary design turbines. Many locations ideal for tidal in-stream power farms around the world are close to rich marine ecology habitats such as marshlands and coral reefs. The rotary design turbines are also static structures, so they hinder navigation of shipping traffic and also marine mammals. These ecosystems are extremely fragile and rely on the marine hydro-kinetic flow to transport nutrients, sediment, gametes, etc. to survive. A number of studies have investigated the effect of tidal power farms on the marine environment and ecology. The short term effects associated with installing individual tidal turbines are well understood and can easily be addressed. However, the long term effects that arise from cumulative action of turbines in a tidal power farm and possibly over a long time are virtually unknown. Any large scale power extraction is likely to alter the flow and thus influence the marine geology and ecology on the long time-scale by modifying the transport of nutrients, sediment, gametes, etc. The modified flow could also effect populations of organisms with a planktonic life stage, and their predators. At this time we have no method for predicting the subsequent evolution of marine habitats, thus the environmental cost of tidal power conversion is unknown.
Because of the large scale design uncertainty and environmental unpredictability with building tidal power farms, the financial risk is sufficiently high that ventures towards large scale farm development are still relatively rare and market penetration is only likely to be successful when a hydro-kinetic conversion technology adequately addresses these uncertainties. The practical and economically sensible strategy for building tidal power farms is through gradual expansion of installed infrastructure whilst continually monitoring the engineering design and environmental impact, and rapidly and cheaply addressing any concerns that arise. Current tidal turbines are not capable of rapid and cheap re-design and therefore are inappropriate for tidal hydro-kinetic energy.
It would therefore be desirable to provide a more efficient and optimized method, apparatus, and system for converting kinetic energy from a fluid flow.